Refine inner-class test @Configuration detection

Update detection logic to also consider `@Rules` classes. Also make the
documentation a little clearer.

Fixes gh-6768

spring-boot-test/src/test/java/org/springframework/boot/test/context/filter/AbstractTestWithConfigAndRunWith.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2012-2016 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.test.context.filter;
+
+import org.junit.runner.RunWith;
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.test.context.junit4.SpringRunner;
+
+/**
+ * Abstract test with nest {@code @Configuration} and {@code @RunWith} used by
+ * {@link TestTypeExcludeFilter}.
+ *
+ * @author Phillip Webb
+ */
+@RunWith(SpringRunner.class)
+public abstract class AbstractTestWithConfigAndRunWith {
+
+	@Configuration
+	static class Config {
+
+	}
+
+}

spring-boot-test/src/test/java/org/springframework/boot/test/context/filter/TestTypeExcludeFilterTests.java

@@ -50,6 +50,14 @@ public class TestTypeExcludeFilterTests {
 				this.metadataReaderFactory)).isTrue();
 	}
 
+	@Test
+	public void matchesNestedConfigurationClassWithoutTestMethodsIfItHasRunWith()
+			throws Exception {
+		assertThat(this.filter.match(
+				getMetadataReader(AbstractTestWithConfigAndRunWith.Config.class),
+				this.metadataReaderFactory)).isTrue();
+	}
+
 	@Test
 	public void matchesTestConfiguration() throws Exception {
 		assertThat(this.filter.match(getMetadataReader(SampleTestConfig.class),